a) Field of the Invention
The present invention is directed to a grating spectrometer system for polychromator spectrometer arrangements and monochromator spectrometer arrangements with more than one light source and a method for the acquisition and evaluation of measurement data.
b) Description of the Related Art
The spectrometer arrangements known from the prior art can be classified into two groups: monochromators and polychromators.
Monochromators make do with only one detector on which the spectral range to be measured is imaged and evaluated successively. However, the time required for measurement is necessarily prolonged and this has particularly disadvantageous results when the sample changes during the measurement period, as is generally the rule in process measurement systems, and when measuring an object in vivo.
In contrast, in polychromators the entire spectral region to be measured is imaged all at once on a detector with a plurality of individual portions and can therefore be measured simultaneously.
An arrangement of this kind comprising a diode array as detector, a concave grating, and a transparent supporting body constructed as a biconvex lens is described, e.g., in DE 40 38 638 A1.
In polychromator spectrometer arrangements, a correspondingly broad-band illumination of the sample is necessary. If one light source is not sufficient for this purpose, illumination by means of a plurality of light sources is also possible.
For this purpose, the light of the different radiation sources is coupled into the beam path. Light is coupled in simultaneously in the solution according to WO 97/35178 A1, but is coupled in successively in DE 198 26 801 A1 and U.S. Pat. No. 5,477,322 A. The advantage in switching on the light sources in succession consists in that scattered light is reduced and the load on the individual light sources is decreased. However, this increases the required measurement time.
Also known from the prior art are polychromators in which the entire spectral region to be imaged is separated into a plurality of diffraction orders. Additional components are required for separating into diffraction orders.
According to US 2004/0257563 A1 and U.S. Pat. No. 5,139,335 A, bandpass filters, for example, can be used for this purpose and must be provided for every diffraction order.
In contrast, the system described in DE 35 16 183 A1 uses a prism for separating the orders.
In the above-mentioned prior art solutions, it is disadvantageous that additional optical components are required for separating orders or for combining the individual light sources, or for both, so that the entire spectrum can be measured simultaneously with polychromator spectrometer arrangements. Other substantial disadvantages include large detector surfaces in polychromator measurement arrangements and long movement paths in monochromator measurement arrangements. This is particularly disadvantageous when only a discontiguous portion of the total spectrum is required for the application, e.g., regions 530 nm to 610 nm, 820 to 850 nm, and 940 to 960 nm, that is, only 130 nm of the total bandwidth of 430 nm are required for the detector surface or movement path.